6502.org Forum Projects Code Documents Tools Forum
It is currently Sat Nov 23, 2024 10:54 pm

View unanswered posts | View active topics


Board index » 6502.org Users Forum » Nostalgia

All times are UTC




Post new topic Reply to topic  Page 4 of 4
  [ 55 posts ]  Go to page Previous  1, 2, 3, 4
  Previous topic | Next topic 
Author Message
JMohan
PostPosted: Wed Feb 07, 2024 8:27 am 
Offline

Joined: Mon Feb 05, 2024 7:06 am
Posts: 9
Hi Neil,
I connected the logic analyser to serial port CH.A coming out of the Digiac board. as I mentioned in a previous post the pinout is non standard pin 1 is TX1 Pin 6 is RX1. I had to make a custom cable which I broke out onto a breadboard so I could connect the ftdi ft232rl adapter and the logic analyser. The chip on the digiac board that handles the serial communication is a motorola mc2681 duart. The output from the duart goes through a max232 ic and int o the serial port.
Top
 Profile  
Reply with quote  
barnacle
PostPosted: Wed Feb 07, 2024 9:09 am 
Offline

Joined: Mon Jan 19, 2004 12:49 pm
Posts: 988
Location: Potsdam, DE
Yup, I suspect you're looking at an inverted RS 232 signal if you're looking at the signal on your breakout box, after the D-9 connector.

But if your FTDI adaptor is an RS232 adaptor and not a UART adaptor, it should correct that apparent inversion (UART can be expected to idle at +5v (or +3v3 for 3v3 systems) while the RS232 signal idles at -3 to -15v)

Neil
Top
 Profile  
Reply with quote  
JMohan
PostPosted: Wed Feb 07, 2024 7:38 pm 
Offline

Joined: Mon Feb 05, 2024 7:06 am
Posts: 9
I measured the voltage at idle at the db9 connector on the digiac it reads -9v

I did some research, apparently you can reprogram the firmware on the ftdi ft232r to invert the tx and rx lines.

after several hours of messing around I reprogrammed my converter with inverted signals.
Now when I try to connect to the digiac via serial it does nothing, the digiac board wont go into terminal mode.
I tested the ftdi adaper by connecting tx and rx together and it works.
I'm running out of ideas.
Top
 Profile  
Reply with quote  
GARTHWILSON
PostPosted: Wed Feb 07, 2024 8:20 pm 
Offline
User avatar

Joined: Fri Aug 30, 2002 1:09 am
Posts: 8546
Location: Southern California
Joseph, it's not clear to me if you understand the difference between just a UART and RS-232 (most accurately "TIA-232," but everyone understands "RS-232").  It's not just about inverting versus not inverting.  RS-232 levels are much higher voltages than just normal logic levels, and they're positive and negative too.  Pretty standard is to go plus and minus twelve volts (although there's a wide acceptable range), to become more immune to noise getting into the line; and connecting an RS-232 output to a standard logic input will probably damage the latter.  I certainly understand the common desire to forgo the RS-232 line drivers and receivers; but unfortunately this has led to confusion and incompatibility, and sometimes damage.  Your FTDI adapter needs to be one that that has the RS-232 line drivers and receivers.  I have a somewhat 65xx-oriented RS-232 primer at http://wilsonminesco.com/RS-232/RS-232primer.html .

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?
Top
 Profile  
Reply with quote  
BigEd
PostPosted: Wed Feb 07, 2024 10:27 pm 
Offline
User avatar

Joined: Thu Dec 11, 2008 1:28 pm
Posts: 10986
Location: England
I'm pretty sure you can get a cheap and cheerful level converter for this situation. (Which also inverts.)

I think I might have one of these - I imagine there are cheaper versions
https://www.sparkfun.com/products/449

Or you can roll your own
http://picprojects.org.uk/projects/simpleSIO/ssio.htm
Top
 Profile  
Reply with quote  
BigDumbDinosaur
PostPosted: Thu Feb 08, 2024 3:41 am 
Offline
User avatar

Joined: Thu May 28, 2009 9:46 pm
Posts: 8513
Location: Midwestern USA
Mohan wrote:
I measured the voltage at idle at the db9 connector on the digiac it reads -9v...

It appears the serial interface on the Digiac unit is TIA-232.

TIA-232 operates at a nominal plus and minus 12 volts DC with respect to ground, with generally-accepted operating conditions supporting a voltage range of 3 to 25 volts.  When the voltage is positive with respect to ground, the TIA-232 circuit is in the “space” condition, which may be thought of as a logic 0.  When the voltage is negative with respect to ground, the circuit is in the “mark” condition, which is considered a logic 1.

On the UART side, a space is zero volts, which is the “opposite” of what is on the TIA-232 side (+3 to +25), but still representing a logic 0.  A mark is a high, generally close to VCC, again the opposite of what is on the TIA-232.

Due to the differences between voltage and polarity on both sides, line drivers, such as the Maxim MAX232 or the older 1488/1489 devices, are required to couple the UART to the TIA-232 link.  The drivers act as level converters and logic inverters at the same time.  As a fairly general rule, you cannot safely connect a TIA-232 circuit directly to a UART—this is aside from the inverted logic meanings.  UARTs operate at 5 or 3.3 volts, always positive with respect to ground.  A TIA-232 circuit operating at full nominal voltage will drive the UART’s inputs well beyond their ratings and likely cause damage.

BigEd wrote:
I'm pretty sure you can get a cheap and cheerful level converter for this situation. (Which also inverts.)

I think I might have one of these - I imagine there are cheaper versions
https://www.sparkfun.com/products/449

Or you can roll your own
http://picprojects.org.uk/projects/simpleSIO/ssio.htm

Those are okay if the only connections you want to make are RxD and TxD.  They have no provisions for CTS/RTS flow-control.  In most cases, attempting to operate above 9600 bpS without hardware flow control will lead to errors during sustained transfers.  As always, caveat emptor!

_________________
x86?  We ain't got no x86.  We don't NEED no stinking x86!
Top
 Profile  
Reply with quote  
barnacle
PostPosted: Thu Feb 08, 2024 6:26 am 
Offline

Joined: Mon Jan 19, 2004 12:49 pm
Posts: 988
Location: Potsdam, DE
I was unable to find either a circuit diagram or a sufficiently clear photo of the Digiac circuit board, but from the photos I did find it looks as if there are two UART-RS232 converter chips between a 40-pin part and the sockets. You could hook a UART signal at their inputs, if this is so.

Neil
Top
 Profile  
Reply with quote  
JMohan
PostPosted: Thu Feb 08, 2024 1:43 pm 
Offline

Joined: Mon Feb 05, 2024 7:06 am
Posts: 9
I'm just going to wait until the serial card that I ordered for my pc to arrive, I'll make a custom cable for it and report back my findings.
Top
 Profile  
Reply with quote  
JMohan
PostPosted: Sat Feb 10, 2024 1:08 pm 
Offline

Joined: Mon Feb 05, 2024 7:06 am
Posts: 9
Attachment:
Digiac_MACIII_6502-first-contact.png
Digiac_MACIII_6502-first-contact.png [ 84.46 KiB | Viewed 1494 times ]


Good news, everyone it is working, I can now communicate with the board via serial terminal.

Thank you all for your advice, suggestions and constructive criticism.
Top
 Profile  
Reply with quote  
BigEd
PostPosted: Sat Feb 10, 2024 1:45 pm 
Offline
User avatar

Joined: Thu Dec 11, 2008 1:28 pm
Posts: 10986
Location: England
That's excellent! I get the impression the serial connection offers some good facilities over and above the keypad options.
Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  Page 4 of 4
  [ 55 posts ]  Go to page Previous  1, 2, 3, 4

Board index » 6502.org Users Forum » Nostalgia

All times are UTC


Who is online

Users browsing this forum: No registered users and 14 guests

You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
6502.org is an ongoing project by Mike Naberezny and contributors.